People in Devon, Cornwall and Somerset have been told to cut down their shower time in order to leave enough water for tourists.
It comes as the region prepares for a summer influx of holidaymakers.
South West Water said it wants people to try to save five litres of water per day in order to maintain reservoir levels.
The company said soaring temperatures, rising numbers of visitors and more people moving to the region are to blame.
It added that because it has been a dry start to the summer people 'need to help save water where they can'.
A South West Water spokesperson said: “We closely monitor our reservoirs all-year round to ensure we have enough water for all our customers and up to 10 million additional users as people come to enjoy the beautiful South West over the summer months.
“We always ask customers to think about their water usage to not just help save water but also help keep bills down.
"On average, a person uses 150 litres of tap water a day, and if every one of our customers saved just 5 litres a day, that would total 10 million litres saved.”
Tourist board data shows that over 200,000 holidaymakers can be in Cornwall at any one time.
There have not been any restrictions on water usage in the region since the drought of 1976 when households went without tap water for hours every day and parts of Devon went 45 days without a single drop of rain.
Surface water sources, such as reservoirs and rivers, provide about 90 per cent of the region’s water supply and it has come close to hosepipe bans in recent years.
How can I save water when gardening?
Use a water butt to collect rainwater – it could fill up with water for free 300 times a year
Use a watering can instead of a hosepipe
It’s best to water plants early in the morning, or in the evening, when it will take longer for it to evaporate
If there is a dry spell, your lawn will not look as lush but it will recover when it rains again. If it needs mowing, set your lawnmower to cut higher and leave clippings where they fall to act as mulch
How can I save water at home?
Turn off the tap while brushing your teeth
Keep a jug of water in the fridge so you don’t have to run your tap cold
Use a bowl for washing up / rinsing fruit and veg – then use this water for plants
Have a shower instead of a bath
Only use your dishwasher or washing machine when you have a full load (this will save money on your energy bills too)
Only fill the kettle with as much water as you need (this will save energy too)
Fix leaking taps and toilets